0 offset is more important
if you insist on 1V across R10 and R11 , just increase both R6 and R7 to ,say,150R
if you insist on 1V across R10 and R11 , just increase both R6 and R7 to ,say,150R
+/- 10% is usual
what's of interest - approx. 1V on one source resistor and 0mV (ref to ground)
(so you just ignore other source resistor reading)
so , two DVM connected and you're good
what's of interest - approx. 1V on one source resistor and 0mV (ref to ground)
(so you just ignore other source resistor reading)
so , two DVM connected and you're good
well, it seems it's going better.
I'm very close to 0, but it changes suddenly from 0 to 10mV, I cant get th 0 offset stable
I'm very close to 0, but it changes suddenly from 0 to 10mV, I cant get th 0 offset stable
input shorted (or volume pot , if mounted,on minimum) , steady temperature conditions
don't breathe around
don't breathe around
Temperature should be Ok, its been woorking about 5 hours
Inputs are not shorted. I have to short IN+ to Ground at the bottom of the PCB. Isn't that?
Thanks!!
Inputs are not shorted. I have to short IN+ to Ground at the bottom of the PCB. Isn't that?
Thanks!!
yup
short in to gnd
where exactly - I don't know , because you didn't post any picture of what you are making
if normal preamp is in question , vol pot on min. is enough
short in to gnd
where exactly - I don't know , because you didn't post any picture of what you are making
if normal preamp is in question , vol pot on min. is enough
Both. I would start over with the biasing procedure that 6l6 has posted earlier in this thread.
Are you at the limit of your pots travel? If you are not and the amp is built correctly you should be sable to achieve proper bias and DC offset. Offset under 100mv is probably fine. But bias must be around 1v.
What value are your pots and what are your mosfets? Did you buy your jfets from a reputable place (not eBay)?
Are you at the limit of your pots travel? If you are not and the amp is built correctly you should be sable to achieve proper bias and DC offset. Offset under 100mv is probably fine. But bias must be around 1v.
What value are your pots and what are your mosfets? Did you buy your jfets from a reputable place (not eBay)?
due to existence of output cap , 0mV offset isn't so important as with DC constructions but - as close as possible to 0mV there, is measure of all things as predicted
as I said - Iq (1V across source resistors) is +/-10% thingie ..... better more than less (as usual in Papaland)
as I said - Iq (1V across source resistors) is +/-10% thingie ..... better more than less (as usual in Papaland)
This is what I'm doing...
6 hours and It's impossible to me to get 0 offset even when I have briged inputs
An externally hosted image should be here but it was not working when we last tested it.
6 hours and It's impossible to me to get 0 offset even when I have briged inputs
There is a reason why there is a cap on output. To get rid of remaining DC. If you can get 1v bias with under 100mv of DC offset you are fine. Once you put the lid on the case it's going to change the DC offset anyways due to temp. The cap will null any DC offset remaining.
Personally, I cannot get below 25mv or so reliably on mine. And when the temp changes offset changes. 100mv or less, probably even 200mv or less is totally ok as long as bias is stable.
Personally, I cannot get below 25mv or so reliably on mine. And when the temp changes offset changes. 100mv or less, probably even 200mv or less is totally ok as long as bias is stable.
Also, check to make sure your mosfets aren't too hot. Those are very small heatsinks. Might be ok though.
My fets are from a reputable sourcen matched very well:
2SK170/2SJ74 matched to 6,67Idss for left channel (both) and 6,67/6,66mA right channel.
Mosfets are 2SK2013/2SJ313 matched to 0,01mA too.
My P1 and P2 are the original 500R value Vishay T73YB501KT20
2SK170/2SJ74 matched to 6,67Idss for left channel (both) and 6,67/6,66mA right channel.
Mosfets are 2SK2013/2SJ313 matched to 0,01mA too.
My P1 and P2 are the original 500R value Vishay T73YB501KT20
I think your amp is fine. No problems. You have to 1v bias and less than 100mv offset, right?
Check to make sure NO DC on output (after the capacitor) and give it a listen. Don't play with p3 yet...it also effects offset.
I really like mine.
Check to make sure NO DC on output (after the capacitor) and give it a listen. Don't play with p3 yet...it also effects offset.
I really like mine.
That will work but you may want to try a heatsink with bigger "fingers" to keep the temp a bit lower. It will be higher inside the chassis. Less temp would be better for the long term but it's fine for now.
DC offset measuring between "D" point and ground is 0
Thanks to all.
I will change heatsinks
Thanks to all.
I will change heatsinks
